1. Field of the Invention
The present invention relates to an improvement in a magnetic amplifying apparatus, and more particularly to a magnetic amplifying apparatus suitable for use as a gate controlling phase shifter for a thyristor or the like.
As is disclosed in the U.S. Pat. No. 4,100,435, for example, a magnetic phase shifter which utilizes an output firing angle of a magnetic amplifier has a convenient function which compares many signals under isolated conditions, amplifies the comparison result, and, after an appropriate time delay, produces an output suited to a gate signal for a semiconductor switching device such as a thyristor or a transistor. In addition, it has a simple and strong structure and is insensitive to noises, which are features inherent in the magnetic amplifier. Accordingly, it has a good reputation as a highly reliable control element.
2. Description of the Prior Art
A magnetic amplifier and a magnetic phase shifter are different from each other only in the way in which an output is utilized and their basic constructions are identical. In the following description, accordingly, the magnetic phase shifter having an expanded application is explained although it may be used as a magnetic amplifier as it is.
The basic construction of the magnetic amplifier or the magnetic phase shifter will now be explained with respect to a half-wave magnetic phase shifter. First, it includes a saturable magnetic core on which an A.C. winding (sometimes referred to as an output winding) and a control winding are wound. A half-wave rectified voltage is applied to the A.C. winding. Applied to the control winding is a D.C. voltage corresponding to a desired phase angle with a polarity opposite to an electromotive force by the A.C. winding.
Basically, with those elements as mentioned above it is possible to take out a phase angle signal indicative of the D.C. voltage applied to the control winding, across the A.C. winding or across a load resistor connected in series with the A.C. winding. During one-half cycle period in which no voltage is applied to the A.C. winding (referred to as a reset period), the magnetic core is magnetized in one polarity by an amount proportional to the magnitude of the D.C. voltage applied to the control winding. During the next one-half cycle period (control period), the magnetic core is magnetized in the opposite polarity by the voltage applied to the A.C. winding. The time period required for the magnetic core to reach saturation is proportional to the reset amount in the previous reset period. Accordingly, the A.C. winding voltage disappears at a phase angle which is proportional to the D.C. control voltage applied to the control winding. This A.C. winding voltage or the voltage across the load resistor connected in series with the A.C. winding is used as the phase angle signal.
As an example, a thyristor connected in an A.C. network which is in synchronism with the half-wave rectified voltage applied to the A.C. winding may be fired directly with the voltage across the load resistor described above. This constitutes a half-wave control rectifying circuit. By combining a plurality of such circuits, any type of thyristor power converter may be phase-controlled.
This type of magnetic phase shifter has a multiple of functions and advantages, such as simplicity and strongness in construction, insensitivity to noises, capability of isolation among multi-signals and capability of comparison, capability of amplification and capability of time delay, etc.
On the other hand, the magnetic phase shifter has disadvantages that it is large in size and expensive in cost. Accordingly, there is recently a tendency to replace the magnetic phase shifter by semiconductor devices.